Display system

ABSTRACT

In a display system capable of displaying images fed from a plurality of sensing devices on an indicator, horizontal and vertical synchronizing signals of the individual measuring devices are synchronized with one another and desired image signals are selected for on-screen presentation during each successive horizontal scanning period, whereby operator-selected multiple images are displayed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to an image displaysystem for displaying image information from measuring equipment, suchas an echo sounder, and more particularly, the invention is concernedwith a display system which can display more than one kind of imageinformation received from a plurality of measuring devices in anintegrated manner.

[0002] Today's modern fishing vessels and pleasure craft are equippedwith a radar 1, a course plotter 2 incorporating, or connected to, aGlobal Positioning System (GPS) receiver, an echo sounder 3, and so on,as shown in FIG. 1. In a conventional onboard system of this kind, adedicated indicator M1 is connected to the radar 1 by three signal linesfor red (R), green (G) and blue (B) signals, signal lines for horizontal(H) and vertical (V) synchronizing signals. Similarly, an indicator M2is connected to the course plotter 2 by its R, G and B signal lines andtwo synchronizing signal lines, while an indicator M3 is connected tothe echo sounder 3 by its R, G and B signal lines and two synchronizingsignal lines.

[0003] Since the aforementioned indicators M1-M3 are usually provided ina ship's bridge, the same number of additional indicators and signallines become necessary if it is desired to monitor the same pictures asshown on the indicators M1-M3 in a remote location, such as a cabin, forexample. The conventional onboard system has therefore been associatedwith the following problems:

[0004] A number of expensive indicators are required.

[0005] It is difficult to provide space for installing such multipleindicators.

[0006] Since three different pictures are individually shown on separatedisplay screens, it is difficult for a viewer to give his or herconsistent attention to the individual pictures, and this would resultin a likelihood that the viewer could overlook important information.

SUMMARY OF THE INVENTION

[0007] This invention is intended to solve the aforementioned problemsof prior art technology. Accordingly, it is an object of the inventionto provide a display system which makes it possible to selectivelypresent one or more images on an indicator by choosing them frommultiple image signals or to set a desired measuring range and otheroperational parameters by making such choice or settings on the relevantindicator.

[0008] In one aspect of the invention, a display system can present asingle image or multiple images on an indicator using image signals fedfrom a plurality of measuring devices.

[0009] To present multiple images on the single indicator, it isessential that image signals from the individual measuring devices bedelivered with precisely controlled timing. For this purpose, thedisplay system comprises a synchronizer for synchronizing horizontal andvertical synchronizing signals of the individual measuring devices withone another.

[0010] The display system also comprises an image selector forselectively switching to desired image signals during each successivehorizontal scanning period or vertical scanning period to make itpossible to present two different images, which are arrangedhorizontally or vertically, for instance, on the indicator screen.

[0011] Horizontally or vertically arranged multiple images can bedisplayed on the indicator by using the image signals, whicheverselected by the image selector, based on the horizontal and verticalsynchronizing signals.

[0012] The images to be displayed can be selected from the indicator ifthere is provided means for transmitting an image selection command fromthe indicator to the image selector.

[0013] When two image signals A, B are selected for the same displayarea of the indicator screen, two different images are superimposed inthat display area. If, however, one of the image signals (image signalA, for example) has a dominantly high signal level, the other imagesignal B would be completely buried. To prevent this from happening, thedisplay system in one varied form further comprises an image priorityallocator which gives first priority to one of the two image signals inselecting a foreground image in image overlay mode. The display systemof this variation makes it possible to clearly present a desired imagein the foreground.

[0014] In another varied form of the display system, control signals forsetting measuring ranges and other operational parameters of themultiple measuring devices are transmitted from the indicator to themeasuring devices through a control line. This makes it possible toremotely control the individual measuring devices from the indicator.

[0015] In still another varied form of the display system, a pluralityof indicators are parallel-connected and image selection commands andmeasuring range setting commands can be transmitted from any of theindicators through a common control line. The display system of thisvariation makes it possible to select desired images and set measuringranges and other operational parameters of the individual measuringdevices from any indicator.

[0016] In another aspect of the invention, a display system can presentimages on a plurality of indicators in different display modes usingimage signals fed from a plurality of measuring devices.

[0017] To make it possible to present different images on the multipleindicators, the display system comprises dedicated image selectorsprovided to the individual indicators. If the image signals are supplieddirectly from the multiple measuring devices to the individualindicators, more than one signal line would be required. To avoid thisinconvenience, the display system of the invention comprises an RGBsignal mixer which combines R, G and B image signals output from each ofthe measuring devices into a single video signal, and each of the imageselectors includes means for separating the combined video signal ofeach measuring device into its original R, G and B image signals.

[0018] These and other objects, features and advantages of the inventionwill become more apparent upon reading the following detaileddescription in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a general system diagram of a conventional onboardsystem comprising a plurality of measuring devices;

[0020]FIG. 2 is a general block diagram of a display system according toa first embodiment of the invention;

[0021]FIG. 3 is a detailed block diagram showing the internalconfiguration of individual measuring devices and a synchronizingcircuit;

[0022]FIGS. 4A to 4E are time charts showing the operation of thesynchronizing circuit of FIG. 2;

[0023]FIG. 5 is a detailed circuit diagram showing the configuration ofan image selection circuit of FIG. 2;

[0024]FIG. 6 is a diagram depicting how image signals of the individualmeasuring devices are combined with one another in the circuit of FIG.5;

[0025]FIG. 7 is a diagram depicting image selecting operation performedby the circuit of FIG. 5;

[0026]FIG. 8 is a diagram showing various display modes provided by thepresent display system;

[0027]FIG. 9 is a diagram showing a relationship between image selectsignals and on-screen display controlled by the circuit of FIG. 5;

[0028]FIG. 10 is a general block diagram of a display system accordingto a second embodiment of the invention;

[0029]FIG. 11 is a block diagram showing the circuit configuration of anRGB signal mixing circuit of FIG. 10;

[0030]FIG. 12 is a diagram showing the operation of the RGB signalmixing circuit of FIG. 11;

[0031]FIG. 13 is a circuit diagram showing the circuit configuration ofone of adders of FIG. 11;

[0032]FIG. 14 is a block diagram showing the circuit configuration ofeach image selection block of FIG. 10;

[0033]FIG. 15 is a diagram showing how an RGB composite signal isseparated into R, G and B signal components by the image selection blockof FIG. 14;

[0034]FIG. 16 is a block diagram of the echo sounder 3 in FIG. 2 or FIG.10 for explaining how a control signal, i.e., a parameter, for example,for varying depth range is transmitted from one of the indicators to theecho sounder to be driven; and

[0035]FIG. 17 is a front view of the indicator shown in FIG. 2 and FIG.10.

PREFERRED EMBODIMENTS

[0036]FIG. 2 is a general block diagram of a display system installedonboard a ship according to a first embodiment of the invention, inwhich elements equivalent to those shown in FIG. 1 are designated by thesame reference numerals or letters.

[0037] Designated by the numeral 10 in FIG. 2 is a synchronizing circuitwhich synchronizes the operational timing of a course plotter 2 and anecho sounder 3 with an internal synchronizing signal of a radar 1. Thecourse plotter 2 incorporates, or is connected to, a GPS receiver.Designated by the numeral 20 is an image selection circuit which selectsone or more desired image signals from those fed from the individualmeasuring devices 1-3 and combines the selected image signals. Indicatedby 30 and 30′ are interconnecting terminal strips, each having aplurality of input terminals IN which are directly connected to theircorresponding output terminals OUT. Indicated by M and M′ are indicatorswhich individually receive R, G and B image signals as well as ahorizontal synchronizing signal H and a vertical synchronizing signal Vfrom the respective interconnecting terminal strips 30, 30′. The twoindicators M, M′ are connected to a common control line CTL which isconnected to the individual measuring devices 1-3 by way of the imageselection circuit 20 and carries signals for switching on-screen imagesand varying measuring ranges and other operational parameters of theindividual measuring devices 1-3.

[0038] In FIG. 2, the indicators M, M′ show examples of split-screenpresentation, each including an echogram produced by the echo sounder 3and shown on right-hand one-third of the full-screen area and a radarpicture produced by the radar 1 and shown on left-hand two-thirds of thefull-screen area. Furthermore, the ship's plotted course L is overlaidon the radar picture.

[0039]FIG. 3 is a detailed block diagram showing the internalconfiguration of the individual measuring devices 1-3 and thesynchronizing circuit 10. In the radar 1, a signal processed by a signalprocessing block 4 is delivered to an image generating block. The imagegenerating block includes a synchronizing signal generator 8 whichreceives a reference clock f1 from a reference clock generator 7 andproduces the horizontal synchronizing signal H and the verticalsynchronizing signal V by means of a 1/n divider and a 1/m divider,respectively. The radar 1 also comprises an image transmitter 9 whichgenerates and transmits R, G and B analog image signals according to thesynchronizing signals H, V.

[0040] The course plotter 2 and the echo sounder 3 comprise respectivesignal processing blocks 5, 6. Signals processed by the signalprocessing blocks 5, 6 are delivered to respective image generatingblocks. These image generating blocks take in the vertical synchronizingsignal V from the radar 1 as a reset signal and individually producehorizontal and vertical synchronizing signals which are synchronizedwith the signals generated in the radar 1. Then, the course plotter 2and the echo sounder 3 generate image signals according to theirsynchronizing signals. The earlier-mentioned synchronizing circuit 10 isa circuit for feeding the vertical synchronizing signal V from the radar1 to the course plotter 2 and the echo sounder 3.

[0041]FIG. 4A shows the vertical synchronizing signal V (period t1), thehorizontal synchronizing signal H (period t2) and RGB image signals ofthe radar 1. As depicted in FIG. 4B, the signals originally produced inthe course plotter 2 have a phase delay of φ1 with respect to thecorresponding signals of the radar 1. Likewise, the signals originallyproduced in the echo sounder 3 have a phase delay of φ2 with respect tothe corresponding signals of the radar 1 as shown in FIG. 4C. When thevertical synchronizing signal V output from the radar 1 is supplied tothe image generating blocks of the course plotter 2 and the echo sounder3 as shown in FIG. 3, the signals of the course plotter 2 and the echosounder 3 are synchronized with the signals of the radar 1 as shown inFIGS. 4D and 4E.

[0042]FIG. 5 is a detailed circuit diagram showing the configuration ofthe image selection circuit 20, in which the radar 1, the course plotter2 and the echo sounder 3 are designated as “devices 1, 2 and 3”,respectively, and designated by 21A, 21B and 21C are image selectionsub-circuits. Since these circuits have a common circuit configuration,their constituent elements are identified by the same alphanumericdesignations. R, G and B signal lines of the individual measuringdevices are connected to transistors TR1, TR2 and TR3, respectively,whose emitters are grounded and bases are connected to output terminalsof respective OR gates OR1.

[0043] Signal lines L_(R), L_(G) and L_(B) from the image selectionsub-circuits 21A and 21B are connected to input terminals of OR gatesOR2 and OR3 and outputs of the OR gates OR2 and OR3 are connected toinput terminals of AND gates AND1 and AND2, respectively. Signal linesfor entering image priority signals P1 and P2 are connected to otherinput terminals of the AND gates AND1 and AND2, respectively. An outputterminal of the AND gate AND1 is connected to an input terminal of theOR gate OR1 of the image selection sub-circuit 21B while an outputterminal of the AND gate AND2 is connected to an input terminal of theOR gate OR1 of the image selection sub-circuit 21A. Further, signallines for entering image select signals S1, S2 and S3 are connected toother input terminals of the OR gates OR1, OR2 and OR3, respectively.

[0044] Besides the aforementioned signal lines L_(R), L_(G) and L_(B),there are provided lines L_(R)′, L_(G)′ and L_(B)′ which are groundedthrough respective load resistors RL. The signal lines L_(R), L_(G) andL_(B) from the device 1 are connected to bases of transistors TR4, TR5and TR6, whose collectors are connected to a supply voltage Vcc andemitters are connected to the lines L_(R)′, L_(G)′ and L_(B)′.

[0045] The devices 2 and 3 are also connected to respective transistorsTR4, TR5 and TR6 of a similar configuration. Each combination of thetransistors TR4, TR5 and TR6 constitutes a buffer circuit. Since thetransistors TR4, TR5 and TR6 connected to the devices 1-3 are connectedto the respective common load resistors RL for the R, G and B lines, Rsignals of the individual devices 1-3 are added together, orsuperimposed, by the transistors TR4 as shown in FIG. 6.

[0046] The image select signals S1, S2, S3 and image priority signalsP1, P2 correspond to display control signals transmitted through thecommon control line CTL shown in FIG. 2, and signals taken from thelines L_(R)′, L_(G)′, L_(B)′ are the R, G and B image signalstransmitted to the interconnecting terminal strips 30, 30′ of FIG. 2.

[0047] Operation of the image selection circuit 20 of FIG. 5 is nowdescribed in detail. The following discussion deals with a case wherethe image select signal S1 is at a Low level, the image select signalsS2 and S3 are at a High level, and the image priority signals P1 and P2at a Low level, as shown in display mode {circle over (1)} of FIG. 8.When the image select signal S1 is at the Low level, an output of theAND gate AND1 (i.e., one of inputs to the OR gate OR1 of the imageselection sub-circuit 21B) is kept continuously at a Low level.Similarly, when the image priority signal P1 is at the Low level, anoutput of the AND gate AND2 (i.e., one of inputs to the OR gate OR1 ofthe image selection sub-circuit 21A) is kept continuously at a Lowlevel.

[0048] When an image select signal is at the Low level, there occurs nochange in the R, G and B image signals transmitted through the relevantsignal lines L_(R),L_(G), L_(B), but when the image select signal isswitched to a High level, the corresponding transistors TR1-TR3 becomeON so that the signal lines L_(R), L_(G), L_(B) are grounded and levelsof the R, G and B image signals carried by these signal lines arezeroed, as shown in FIG. 7. Therefore, in display mode {circle over (1)}of FIG. 8, the R, G and B image signals from only the device 1 (radar)are transmitted to the lines L_(R)′, L_(G)′, L_(B)′ and the indicatorsM, M′ present only a radar picture.

[0049] In FIG. 8, only the image select signal S2 is at the Low level indisplay mode {circle over (2)} while only the image select signal S3 isat the Low level in display mode {circle over (3)}. Accordingly, theindicators M, M′ present only an image fed from the device 2 (courseplotter) in display mode {circle over (2)}, only an echogram fed fromthe device 3 (echo sounder) in display mode {circle over (3)}.

[0050] In display mode {circle over (4)} of FIG. 8, the image selectsignal S3 is at the High level while the image select signals S1, S2 areat the Low level so that the R, G and B image signals from the device 3(echo sounder) are suppressed while the R, G and B image signals fromthe radar 1 and the course plotter 2 are transmitted to the linesL_(R)′, L_(G)′, L_(B)′. If both of the image priority signals P1, P2 areset to the Low level, the image signals from the radar 1 and the courseplotter 2 are superimposed with each other. If, however, the imagepriority signals P1, P2 are set to the High and Low levels,respectively, as shown in display mode {circle over (4)} of FIG. 8, oneinput terminal of the AND gate AND1 becomes High. On the other hand, ifany of the signal lines L_(R), L_(G), L_(B) of the device 1 is at theHigh level, an output terminal of the OR gate OR2 (i.e., the other inputterminal of the AND gate AND1) becomes High so that the image selectsignal S1 at the High level is supplied to one input terminal of the ORgate ORI of the image selection sub-circuit 21B (with the image selectsignal S2 fed to the other input terminal set at the Low level) and theR, G and B image signals from the device 2 (course plotter) aresuppressed. This means that the image signals from the device 2 (courseplotter) are suppressed only when the image signals from the device 1(radar) contain any picture information with first priority given to theradar picture.

[0051] If the image priority signal P1 is at the Low level and the imagepriority signal P2 is at the High level as shown in display mode {circleover (5)} of FIG. 8, a course plot picture is presented with priorityover the radar picture.

[0052] In display modes {circle over (1)} to {circle over (5)} above,each image select signal is kept at the High or Low level throughouteach successive horizontal scanning period. FIG. 9 shows a varied modeof presentation, in which a radar picture and an echogram aresimultaneously displayed side by side. This is achieved by switching theimage select signal S1 from the Low level to the High level and theimage select signal S3 from the High level to the Low level at the sametime during each successive horizontal scanning period as illustrated.An example of this kind of presentation is shown as display mode {circleover (6)} in FIG. 8. If the levels of the image select signals S1 and S2are switched in a similar way, a course plot picture and an echogramwill be displayed side by side as shown in display mode {circle over(7)} of FIG. 8.

[0053] In a case where the indicator M has a vertically elongate screen,it is possible to simultaneously present different images in upper andlower portions of the screen by switching the levels of the appropriateimage select signals during each successive vertical scanning period.

[0054] If the course plot picture is superimposed on the radar pictureof display mode {circle over (6)} with priority given to the course plotpicture, three images (radar, course plot and echogram) are displayed atthe same time.

[0055] The display system so far described can present images fed fromthe individual measuring devices 1-3 in various display modes as shownin FIG. 8 on the indicators M, M′ of FIG. 2 by transmitting theappropriate display control signals to the image selection circuit 20through the common control line CTL. It is also possible to remotely setthe measuring ranges and other operational parameters of the measuringdevices 1-3 from the individual indicators M, M′ by transmitting controlsignals associated with addresses designating the desired destinationdevices, i.e., the radar 1, the course plotter 2 and the echo sounder 3,as appropriate. While the indicators M, M′ present the same picture inthe above-described configuration of FIG. 2, it may be modified topermit presentation of different pictures on the individual indicatorsM, M′. This is accomplished by a display system according to a secondembodiment of the invention, which is shown in FIG. 10.

[0056] In the display system of FIG. 10, the indicators M, M′ areprovided with respective image selection blocks 50, which perform thesame functions as the image selection circuit 20 of FIG. 2, to make itpossible to present different pictures on the individual indicators M,M′. This display system requires somewhat complex wiring compared to theconfiguration of FIG. 2, because it would be necessary to connect threeeach signal lines (R, G and B) from the radar 1, the course plotter 2and the echo sounder 3 to the individual image selection blocks 50 as inthe configuration of FIG. 1. More specifically, at least nine coaxialcables would be required as the R, G and B signal lines.

[0057] To reduce this complexity in wiring, the display system of FIG.10 has an RGB signal mixing circuit 40 for combining three each signallines from the radar 1, the course plotter 2 and the echo sounder 3 intoa single signal line (three signal lines in total for the measuringdevices 1-3).

[0058]FIG. 11 shows the circuit configuration of the RGB signal mixingcircuit 40, in which designated by the numeral 11 are signal adders foradding a horizontal synchronizing signal H and a vertical synchronizingsignal V to R and B image signals fed from the radar 1, respectively.Designated by the numeral 12 are signal multipliers which performfrequency conversion by multiplying R, G and B image signals from theradar 1, the course plotter 2 and the echo sounder 3 by carriers offrequencies f7, f8 and f9, respectively. When the carrier of frequencyf7 is modulated by a signal having a bandwidth of fs, upper sidebandcomponents falling within a frequency band of fc+fs and lower sidebandcomponents falling within a frequency band of fc-fs are obtained asshown in FIG. 12. Designated by the numeral 13 are bandpass filterswhich permit only the upper sideband components to pass through. Asshown in FIG. 11, there are provided three bandpass filters 13 havingcenter frequencies of f4, f5 and f6 for each of the measuring devices1-3. Designated by the numeral 14 are adders for combining the uppersideband components which have passed through the bandpass filters 13 ofR, G and B channels. FIG. 13 shows the circuit configuration of eachadder 14, in which output signals of the bandpass filters 13 are addedtogether by a combination of three transistors t. Referring again toFIG. 11, designated by the numeral 15 are buffer amplifiers whichamplify combined, or composite, video signals of the radar 1, the courseplotter 2 and the echo sounder 3 and deliver the amplified video signalsthrough low-impedance output circuits. The composite video signals ofthe radar 1, the course plotter 2 and the echo sounder 3 thus obtainedin the RGB signal mixing circuit 40 are transmitted to interconnectingterminal strips 30, 30′.

[0059]FIG. 14 shows the circuit configuration of each image selectionblock 50. The composite video signals of the radar 1, the course plotter2 and the echo sounder 3 delivered through the interconnecting terminalstrip 30 are fed into bandpass filters 51 having center frequencies off4, f5 and f6 (which are equal to those shown in FIG. 11), respectively.As a consequence, the individual composite video signals are separatedinto R, G and B image signals as shown in FIG. 15 and these imagesignals are fed into an image selection circuit 52. The image selectioncircuit 52 performs the same function as the image selection circuit 20of FIG. 2. It can present images fed from the individual measuringdevices 1-3 in various display modes as shown in FIG. 8 on the relevantindicator M, M′ by selecting and combining the desired image signals. InFIG. 10, the indicator M presents an echogram fed from the echo sounder3 at the right of the screen and a radar picture at the left of thescreen with a plotted course L of a ship overlaid on the radar picture.On the other hand, the indicator M′ presents only a combination of thefrom an indicator.

[0060] Referring to FIGS. 16 and 17, there will be explained,particularly, how a control signal, i.e., a parameter, for example, forvarying measurement range of the echo sounder 3 is transmitted from oneof the indicators M, M′ and how the echo sounder operates in responsethereto.

[0061] The echo sounder 3 comprises a controller 101, a transmissionsignal generator 102, a search pulse generator 103, an ultrasoundtransducer 104, an amplifier 105, an analog-to-digital converter 106 anda memory unit 107.

[0062] On the panel of the indicator, there are arranged key switches111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122 and 123.

[0063] For instance, underwater conditions in a depth range of 0 to 100meters are at an initial stage displayed on the indicator. When thedepth range is desired to be changed to another search range 0 to 200meters, the key 116 is first pressed down so that a signal having anID-number “1 +116” is transmitted to a main processor (not shown) whichtransmits a control signal to the echo sounder 3 to place the echosounder in an condition in which an operating parameter is changed.Then, the key 122 is pushed down so that a signal having an ID-number “1+122” is transmitted to the main processor. When the key 116 is againpushed down, the main processor transmits a range control signal to theecho sounder 3. The controller 101 controls in response to the rangecontrol signal the transmission signal generator 102 and the A/Dconverter 106. The transmission signal generator 102 produces a pulsesignal. The search pulse generator 103 generates a search signal havinga carrier frequency modulated by the pulse. The search signal istransmitted into the water by means of the ultrasound transducer 104.Echo signals are received by the transducer 104 and are amplified by theA/D converter 106. Resultant digital signals are written into the memoryunit 107. The signals stored in the memory are read out and transmittedto the indicator M so that underwater conditions in the depth range of 0to 200 meters are displayed on the indicator M.

What is claimed is:
 1. A display system for displaying images fed from aplurality of measuring devices, said display system comprising: asynchronizer for synchronizing horizontal and vertical synchronizingsignals of the individual measuring devices with one another; an imageselector for selecting desired image signals from those fed from theindividual measuring devices during each successive horizontal scanningperiod or vertical scanning period; and an indicator for simultaneouslydisplaying a plurality of images obtained from the selected imagesignals by arranging the images horizontally or vertically based on thehorizontal and vertical synchronizing signals; wherein an imageselection command is transmitted from said indicator to said imageselector.
 2. A display system according to claim 1 further comprising animage priority allocator which gives first priority to one of two imagesignals in selecting a foreground image in an image overlay mode inwhich the two image signals are selected at the same time and combinedduring a specified portion of each successive scanning period.
 3. Adisplay system according to claim 1 or 2 wherein control signals forsetting parameters of the individual measuring devices are transmittedfrom said indicator through a control line.
 4. A display systemaccording to claim 3 wherein a plurality of indicators areparallel-connected and image selection commands and parameter settingcommands can be transmitted from any of said indicators through a commoncontrol line.
 5. A display system for displaying images fed from aplurality of measuring devices, said display system comprising: asynchronizer for synchronizing horizontal and vertical synchronizingsignals of the individual measuring devices with one another; an RGBsignal mixer for combining R, G and B signals output from each of saidmeasuring devices into a single video signal; an image selector whichseparates the combined video signal of each measuring device into itsoriginal R, G and B signals and selects desired image signals from thosefed from the individual measuring devices during each successivehorizontal scanning period or vertical scanning period; and a pluralityof indicators; wherein parameters of the individual measuring devicescan be set from any of said indicators through a common control line. 6.A display system according to claim 3, 4 or 5 wherein a parameter is ameasuring range.
 7. A display system for displaying images comprising: aplurality of measuring devices; an image selector for selecting; and anindicator for displaying an image obtained from the selected imagesignal; wherein an image selection command is transmitted from saidindicator to said image selector and a parameter is transmitted fromsaid indicator to one of said plurality of measuring devices.
 8. Adisplay system comprising: a plurality of measuring devices; a pluralityof indicators for displaying images obtained from said plurality ofmeasuring devices; wherein a parameter is transmitted to a desired oneof the measuring devices from at least one of the indicators.
 9. Adisplay system for displaying images fed from two or three of a radar, aplotter and an echo sounder, said display system comprising: a pluralityof indicators for displaying images obtained from said one or two orthree measuring devices; wherein a parameter is transmitted to a desiredone of the measuring devicesfrom at least one of the indicators.